Temprature compensated chemical mechanical polishing apparatus and method

ABSTRACT

A chemical mechanical polishing (CMP) system ( 22 ) having a radiant heating apparatus ( 30 ) for direct radiant heating of the polishing surface ( 26 ) of the polishing pad ( 16 ). Radiant energy ( 28 ) is impinged onto a selected area of the polishing surface to provide temperature compensation of the material removal rate across the surface ( 24 ) of the wafer ( 14 ). The radiant energy may be in the form of infrared radiation, a laser beam or microwave energy. The power level, angle of impingement, duration of exposure and footprint of the radiant energy may be controlled to achieve a desired temperature gradient on the polishing surface. The temperature of the polishing surface may further be regulated by impinging a temperature conditioning gas ( 32 ) onto the polishing surface.

FIELD OF THE INVENTION

[0001] This invention relates generally to the field of semiconductordevice fabrication, and more particularly, to the field of chemicalmechanical polishing of semiconductor wafers.

BACKGROUND OF THE INVENTION

[0002] The fabrication of microelectronics devices involves thedeposition and removal of multiple layers of material on a semiconductorsubstrate to form active semiconductor devices and circuits. Suchdevices utilize multiple layers of metal and dielectric materials thatcan selectively connect or isolate device elements within a layer andbetween layers. Integrated circuits using up to six levels ofinterconnects have been reported and even more complex circuits areexpected in the future. Device geometries have gone from 0.50 micron to0.12 micron and will soon be 0.08 micron. Multi-levels of metallizationare required in such devices. With these reductions in device geometry,each inter-metal level must be planarized before forming a subsequentlevel. The generally accepted process for creating sufficiently planarsurfaces is chemical mechanical polishing (CMP). CMP may be used toremove high topographic variations and to remove defects, scratches orembedded particles from the surface of a semiconductor wafer.

[0003] The CMP process generally involves rubbing a surface of asemiconductor wafer against a polishing pad under controlled pressure,temperature and rotational speed in the presence of a chemical slurry.An abrasive material is introduced between the wafer and the polishingpad, either as particles affixed to the polishing pad itself or in fluidsuspension in the chemical slurry. The chemical and abrasive combinationfunctions to to remove a portion of the surface of the wafer in apolishing action. The slurry movement assures temperature control andfacilitates the movement of the polishing debris away from the wafer.

[0004] As may be seen in FIG. 1, a chemical mechanical polishing system10 may include a carrier 12 for holding and moving a semiconductor wafer14 against a polishing pad 16 supported on a rotatable platen 18. Slurry20 is used to provide the desired chemical interaction and abrasion whenthe wafer 14 is pressed and rotated against the polishing pad 16. Therate of material removal from the wafer 14 will depend upon manyvariables, including the amount of force F exerted between the wafer 14and the polishing pad 16, the speeds of rotation R₁ of the carrier andR₂ of the platen, the transverse location of the carrier 12 relative tothe axis of rotation of the platen 18, the chemical composition of theslurry 20, the temperature, and the composition and history of use ofthe polishing pad 16. Numerous configurations of CMP machines are knownand are available in the industry. One manufacturer of such CMP machinesis Applied Materials, Inc. of Santa Clara, Calif.(www.appliedmaterials.com) One manufacturer of polishing pads is Rodel,Inc. of Phoenix, Ariz. (www.rodel.com)

[0005] A known difficulty with CMP operations is that the rate ofmaterial removal may be uneven across the surface of the wafer 14. U.S.Pat. No. 5,873,769 issued to Chiou, et al., describes a method andapparatus for achieving a uniform removal rate across the surface of awafer. Chiou describes dividing both the platen and the carrier intoconcentric circular segments, and controlling the temperature of thevarious segments to adjust the rate of removal of material across thesurface of the wafer. Chiou describes the use of multiple electricheating elements for controlling the temperature of the respectivemultiple circular segments. Alternatively, Chiou describes the use ofmultiple tubes in the platen and carrier for delivering fluid that isheated or cooled to a desired temperature. Such a system requires alarge amount of energy to heat the platen and the carrier. Furthermore,because of the thermal inertia of these structures, the system of Chioumay not respond as quickly as desired to a required change intemperature. The segmented and heated platen and carrier are moreexpensive to manufacture and maintain than non-segmented, non-heatedcomponents. Finally, the definition of the number and location of thesegments is fixed and can not be changed without a correspondingequipment redesign.

[0006] In a further embodiment, Chiou describes the use of a polishingpad with multiple concentric grooves and the supply of polishing slurryto the various grooves at various different temperatures to effect thedesired temperature compensation. This embodiment suffers from many ofthe same limitations as the segmented carrier/platen embodiment. Aspecial pad design is required, and the definition of the number andlocation of the grooves can not be easily changed. The abrasive slurrysupply system is necessarily more complicated and expensive tomanufacture, to operate and maintain than would be the traditionalsingle supply system. The transient response time of this embodiment isalso limited by whatever system is used to heat the slurry and by thetransit time of the slurry from the point of heating to the polishingpad grooves. Furthermore, this design would be of no use in a systemthat does not utilize a slurry for abrasion or material removal.Accordingly, an improved apparatus and method is needed for controllingthe material removal rate across the surface of a wafer during achemical mechanical polishing operation.

SUMMARY OF THE INVENTION

[0007] A device for polishing a wafer is described herein as including:a polishing pad having a polishing surface; a wafer carrier adapted tourge a surface of a wafer against the polishing surface; and a radiantheating apparatus impinging radiant energy onto the polishing surfaceremote from the surface of the wafer. The radiant heating apparatus maybe a source of infrared radiation, a laser, or a source of microwaveenergy. The radiant heating apparatus may be disposed in a predeterminedposition with respect to the polishing surface to establish apredetermined radiant energy footprint on the polishing surface.

[0008] In a further embodiment, a device for polishing a wafer isdescribed as including: a polishing pad having a polishing surface; awafer carrier adapted to urge a surface of a wafer against the polishingsurface; and a means for applying heat energy directly to the polishingsurface remote from the surface of the wafer.

[0009] Further, a device for polishing a wafer is described asincluding: a polishing pad having a polishing surface; a wafer carrieradapted to urge a surface of a wafer against the polishing surface; anda flow of a temperature conditioning gas directed onto the polishingsurface. The flow of temperature conditioning gas may be provided at atemperature greater than or less than a temperature of the polishingsurface. The device may further include a radiant heating apparatusimpinging radiant energy onto the polishing surface remote from thesurface of the wafer.

[0010] A method of polishing a wafer is described herein as including:providing a polishing pad having a polishing surface; urging a wafersurface against the polishing surface while providing relative motionthere between; and impinging the polishing surface with radiant energyat a location remote from the wafer surface to regulate a polishingsurface temperature. The intensity of the radiant energy may be variedduring the step of impinging. The radiant energy may be applied prior toand/or during the step of urging. The radiant energy may be infraredradiation, laser energy, and/or microwave energy. A predeterminedradiant energy footprint may be projected onto the polishing surface toeffect a desired temperature gradient.

[0011] An alternate method of polishing a wafer is described asincluding the steps of: providing a polishing pad having a polishingsurface; urging a wafer surface against the polishing surface whileproviding relative motion there between; and impinging the polishingsurface with at least one of radiant energy and a temperatureconditioning gas remote from the wafer surface to regulate a polishingsurface temperature.

BRIEF DESCRIPTION OF THE INVENTION

[0012] The features and advantages of the present invention will becomeapparent from the following detailed description of the invention whenread with the accompanying drawings. Like numerals are used to designatesimilar components in multiple figures.

[0013]FIG. 1 is a schematic illustration of a prior art chemicalmechanical polishing system.

[0014]FIG. 2 is a schematic illustration of a chemical mechanicalpolishing system including a radiant heating apparatus impinging radiantenergy onto the polishing surface of the polishing pad and a conditionedgas supply impinging a conditioned gas upon the polishing surface.

DETAILED DESCRIPTION OF THE INVENTION

[0015]FIG. 2 is a schematic illustration of a chemical mechanicalpolishing apparatus 22 providing localized temperature compensation forcontrolling the material removal rate across the surface of a waferbeing polished. The polishing apparatus 22 contains many components thatare similar to those of the prior art apparatus 10 illustrated inFIG. 1. A polishing pad 16 is disposed over a rotatable platen 18. Awafer 14 having a surface to be polished 24 is urged against a polishingsurface 26 of the polishing pad 16 by a rotatable carrier 12. Chemicalslurry 20 containing abrasive particles is delivered to the polishingsurface 26 to provide the desired polishing action. The term polishingsurface as used herein includes not only a top-most layer of thepolishing pad 16 but also any portion of the slurry 20 entrainedthereon.

[0016] The temperature of at least a portion of the polishing surface 26may be increased by the direct impingement of radiant energy 28 onto thepolishing surface 26. The term direct (or directly) as used hereinrefers to the application of heat energy to the top polishing surface 26without applying the heat energy through the thickness of the polishingpad 16, as is done in the prior art systems. The polishing surface 26may be heated in an area remote from the area of contact with the wafersurface 24. By controlling the area exposed to the radiant energy 28,one may induce a change in the temperature profile of the polishingsurface 26 across the wafer surface 24 as the heated portion of thepolishing surface 26 is rotated to be in contact with the wafer 14. Achange in the temperature of the polishing pad material will alter thehardness of the pad material, thereby changing the visco-elasticcharacteristics and wafer material removal rate of the pad in thatlocalized area. Every visco-elastic material has a stress-straincharacteristic that is dependent upon the temperature of the material.The stress-strain characteristic defines the rate of deformation(deformation per unit time) upon the relaxation of the applied stressresulting from the down force during the polishing operation. Thetemperature of the pad material directly impacts this relaxation. Paddeformation is, in turn, related to the amount of reaction force that isexerted onto the abrasive material in the slurry and upon the raisedareas of the surface being polished. The reaction force determines themechanical component of the CMP process, thereby impacting the materialremoval rate. Thus, the application of radiant energy 28 to thepolishing surface 26 provides a mechanism for temperature compensationof the wafer material removal rate. For most pad/slurry applications, anincrease in the temperature is expected to increase the material removalrate during a CMP operation. However, one skilled in the art willappreciate that the response of the material removal rate to a change intemperature must be evaluated for each particular pad/slurryapplication.

[0017] The radiant energy 28 is provided by a radiant heating apparatus30. The radiant heating apparatus 30 is located proximate the polishingpad opposed the platen 18, thereby avoiding the need for conductiveheating of the polishing surface 26. By applying the energy 28 directlyonto the polishing surface 26, it is possible to affect the materialremoval rate without heating of the entire platen 18 and without heatingthe entire thickness of the polishing pad 16 to the desired temperature.Accordingly, a relatively low amount of energy 28 is needed to achieve adesired temperature rise. It may be desired to achieve a temperaturerise of up to 90° C. or preferably in the range of 20-60° C. above theambient temperature.

[0018] The proximity of the radiant heating apparatus 30 to thepolishing surface 26 may vary depending upon the particular design ofthe CMP apparatus 22. Furthermore, the proximity of the radiant heatingapparatus 30 may vary depending upon the type and power level of radiantenergy 28 utilized. The radiant heating apparatus 30 is located at anydistance from the polishing surface 26 appropriate for exposing thesurface to a desired energy flux. In one embodiment, the means forproviding the radiant heating may be a source of infrared radiation,such as a heat lamp located directly above the polishing surface 26. Ina further embodiment, a laser may be used to provide the radiant energy28, with the delivery of the laser energy being through a conventionalmirror system or through an optical fiber. Due to the congruence of alaser beam, it may be possible to locate the source of the laser energyat a greater distance away from the polishing pad 16 than would bepossible with an infrared radiation source. Alternatively, a microwaveradiation source may be used at any desired frequency or combination offrequencies. One or more such sources of radiant energy may be usedsingly or in combination.

[0019] The radiant heating apparatus 30 may be placed in a predeterminedposition with respect to the polishing surface 26 in order to impingeenergy onto a predetermined energy footprint on the polishing surface26. A change in energy intensity across the footprint may be achieved bylocating the radiant heating apparatus 30 at an appropriate angle withrespect to a plane of the polishing surface 26. Such an energy gradientwill generate a corresponding change in the temperature rise generatedin the polishing surface 26 across the footprint. Furthermore, a lens orother beam-spreading device may be used to accomplish a desired energygradient across the footprint. In one embodiment, only an edge portionof the polishing surface 26 is heated. In other embodiments, variousother portions of the polishing surface 26 may be heated. More than oneportion of the polishing surface 26 may be heated to the same ordiffering temperatures.

[0020] The operation of chemical mechanical polishing apparatus 22provides a high degree of flexibility for temperature compensation ofthe CMP process. In one embodiment, radiant heating apparatus 30 may beoperated for a predetermined period of time at a predetermined powerlevel as the platen 18 is rotated prior to the wafer 14 being broughtinto contact with the polishing pad 16. This would allow a selected areaof the polishing surface 26 exposed to the energy footprint to bebrought to a desired temperature prior to initiating the polishingaction. The flux of energy 28 may then be terminated and the radiantheating apparatus 30 moved away from the platen 18 in order to protectit from possible exposure to splashing of the slurry 20. Alternatively,the radiant energy 28 may be initiated concurrently with the polishingactivity, and/or the energy 28 may continue to impinge upon thepolishing surface 26 during the polishing process.

[0021] It is also possible to change the power level of the radiantheating apparatus 30 at various times before and throughout thepolishing process. For example, a first power level may be used topre-heat the polishing surface 26 prior to the initiation of the flow ofslurry 20, then a second power level may be used to maintain a desiredtemperature after the slurry 20 begins to flow. Changes in temperaturemay be quickly achieved due to the low thermal inertia of the polishingsurface 26, since there is no need to change the temperature of theplaten 18 or the entire thickness of the polishing pad 16.

[0022] The location of the impingement of energy 28 may be changed as aCMP process progresses, or it may be changed in response to a changedpolishing requirement. The operation of the radiant heating apparatus 30may be controlled manually or by an automatic control system responsiveto a measurement of the temperature of the polishing surface 26 and/orto any other appropriate control parameter. Such control parameters maybe determined by developing correlations between measurable parameterssuch as removal rate, removal uniformity or slurry composition, and theymay be used as a tool for generating an appropriate control response.For example, removal rates may be measured for sequential polishingexperiments. The effect of temperature can be correlated to the amountof material removed and the removal rate during such sequentialpolishing operations. A feedback loop incorporating such correlationsmay be used as a calibration tool for temperature control.

[0023] The polishing surface temperature may also be regulated byimpingement of a temperature conditioning gas 32 onto polishing surface26. The gas 32 may be air or other gas compatible with the polishingoperation, and it may be supplied from a gas conditioning apparatus 34such as a heater, air conditioner, or combined heating-ventilating-airconditioning (HVAC) system. The gas 32 may be supplied from conditioningapparatus 34 at a temperature greater than or less than the temperatureof the polishing surface 26. Accordingly, temperature conditioning gas32 serves to add or to remove heat energy directly to/from the surface26 of pad 16 in order to raise or lower the temperature of at least aportion of the polishing surface 26 to a predetermined temperature.Temperature conditioning gas 32 may be used together with or separatelyfrom radiant energy 28 to effect a desired temperature control scheme.

[0024] While the preferred embodiments of the present invention havebeen shown and describe herein, it will be obvious that such embodimentsare provided by way of example only. Numerous variations, changes andsubstitutions will occur to those of skill in the art without departingfrom the invention herein. Accordingly, it is intended that theinvention be limited only by the spirit and scope of the appendedclaims.

I claim as my invention:
 1. A device for polishing a wafer, the devicecomprising: a polishing pad having a polishing surface; a wafer carrieradapted to urge a surface of a wafer against the polishing surface; anda radiant heating apparatus positionable to provide radiant energy ontothe polishing surface remote from the surface of the wafer.
 2. Thedevice of claim 1, wherein the radiant heating apparatus comprises asource of infrared radiation.
 3. The device of claim 1, wherein theradiant heating apparatus comprises a laser.
 4. The device of claim 1,wherein the radiant heating apparatus comprises a source of microwaveenergy.
 5. The device of claim 1, wherein the radiant heating apparatusis disposed in a predetermined position with respect to the polishingsurface to establish a predetermined radiant energy footprint on thepolishing surface.
 6. A device for polishing a wafer, the devicecomprising: a polishing pad having a polishing surface; a wafer carrieradapted to urge a surface of a wafer against the polishing surface; anda means for applying heat energy directly to the polishing surface froma source remote from the surface of the wafer.
 7. The device of claim 6,wherein the means for applying heat energy further comprises a flow of atemperature conditioning gas directed onto the polishing surface.
 8. Thedevice of claim 7, wherein the flow of temperature conditioning gas isprovided at a temperature greater than a temperature of the polishingsurface.
 9. The device of claim 7, wherein the flow of temperatureconditioning gas is provided at a temperature less than a temperature ofthe polishing surface.
 10. The device of claim 7, further comprising aradiant heating apparatus impinging radiant energy onto the polishingsurface remote from the surface of the wafer.
 11. A method of polishinga wafer, the method comprising: providing a polishing pad having apolishing surface; urging a wafer surface against the polishing surfacewhile providing relative motion there between; and impinging thepolishing surface with radiant energy at a location remote from thewafer surface to regulate a polishing surface temperature.
 12. Themethod of claim 11, further comprising varying an intensity of theradiant energy during the step of impinging.
 13. The method of claim 11,further comprising impinging the at least a portion of the polishingsurface with radiant energy prior to the step of urging.
 14. The methodof claim 11, further comprising impinging the at least a portion of thepolishing surface with radiant energy during the step of urging.
 15. Themethod of claim 11, wherein the step of impinging further comprisesexposing the at least a portion of the polishing surface to infraredradiation.
 16. The method of claim 11, wherein the step of impingingfurther comprises exposing the at least a portion of the polishingsurface to laser energy.
 17. The method of claim 11, wherein the step ofimpinging further comprises exposing the at least a portion of thepolishing surface to microwave energy.
 18. The method of claim 11,further comprising disposing a source of radiant energy at apredetermined position in relation to the polishing surface in order toestablish a predetermined radiant energy footprint on the polishingsurface.
 19. A method of polishing a wafer, the method comprising:providing a polishing pad having a polishing surface; urging a wafersurface against the polishing surface while providing relative motionthere between; and impinging the polishing surface with at least one ofradiant energy and a temperature conditioning gas remote from the wafersurface to regulate a polishing surface temperature.
 20. The method ofclaim 19, further comprising impinging only an edge portion of thepolishing surface with the at least one of radiant energy and atemperature conditioning gas.